Allow libc++ to be built on systems without POSIX threads

If you're crazy enough to want this sort of thing, then add
-D_LIBCPP_HAS_NO_THREADS to your CXXFLAGS and
--param=additiona_features=libcpp-has-no-threads to your lit commnad line.

http://reviews.llvm.org/D3969


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@217271 91177308-0d34-0410-b5e6-96231b3b80d8

src/algorithm.cpp

@@ -47,12 +47,16 @@ template bool __insertion_sort_incomplete<__less<long double>&, long double*>(lo
 
 template unsigned __sort5<__less<long double>&, long double*>(long double*, long double*, long double*, long double*, long double*, __less<long double>&);
 
+#ifndef _LIBCPP_HAS_NO_THREADS
 static pthread_mutex_t __rs_mut = PTHREAD_MUTEX_INITIALIZER;
+#endif
 unsigned __rs_default::__c_ = 0;
 
 __rs_default::__rs_default()
 {
+#ifndef _LIBCPP_HAS_NO_THREADS
     pthread_mutex_lock(&__rs_mut);
+#endif
     __c_ = 1;
 }
 
@@ -63,8 +67,12 @@ __rs_default::__rs_default(const __rs_default&)
 
 __rs_default::~__rs_default()
 {
+#ifndef _LIBCPP_HAS_NO_THREADS
     if (--__c_ == 0)
         pthread_mutex_unlock(&__rs_mut);
+#else
+    --__c_;
+#endif
 }
 
 __rs_default::result_type